The present invention relates to light-sensitive, perfluoroalkyl-group containing 1,2-naphthoquinone diazide compounds and to light-sensitive reproduction materials which comprise these compounds and are suitable for use in the production of printing plates for waterless offset printing.
Other than in the customarily used offset-printing process, where differentiation between image areas and non-image areas during printing is effected by the simultaneous action of water or water-containing liquids, on the one hand, and printing ink, on the other hand, differentiation in waterless planographic printing, particularly offset printing, normally results from the fact that the ink-receptive areas and the ink-repellent areas (which are not moist with water) on a printing plate surface show different interactions with the printing ink. From the state of the art, the following publications are known, which deal with this subject:
U.S. Pat. No. 3,677,178 discloses a printing plate in which a support material comprising a metal, a plastic, or paper is coated with a layer of a hydrophobic and oleophobic silicone rubber and a radiation-sensitive reproduction layer, in the indicated or in the reverse order. As the radiation-sensitive compound, the reproduction layer contains ammonium dichromate, formaldehyde condensates of diphenylamine-4-diazonium salts, or polyvinyl cinnamate. In the printing process, the ink-receptive areas either comprise bared portions of the support material or portions of the reproduction layer which have been cured by irradiation.
In the printing plate according to U.S. Pat. No. 3,511,178 and U.S. Pat. No. 3,682,633, the support material is first coated with a radiation-sensitive reproduction layer and then with a coating having a lower release value (reduced adhesive interaction) with respect to printing inks than the support material. The last-mentioned coating either comprises of polysiloxane (silicone elastomer) or a fluorine-containing organic compound, for example, a homopolymer of the methacrylic acid ester of perfluorooctanol.
Further embodiments of printing plates for waterless offset-printing and of compounds which are suitable for use in printing plates of this kind are, for example, disclosed in the following publications:
In German Offenlegungsschrift No. 25 24 562 (equivalent to British Pat. No. 1,501,128) radiation-sensitive coatings are described, which comprise an aromatic diazonium cation, an anion of a carboxylic acid or sulfonic acid containing perfluoroalkyl groups and, optionally, a polymeric organic binder. It is stated that these layers can be used for printing directly after irradiation, i.e., a developing step is not required.
Published European Patent Application No. 0,037,094, discloses that it is possible to prepare radiation-sensitive polymers which contain copolymers of (a) acrylic or methacrylic acid perfluoroalkyl esters and (b) acrylic or methacrylic acid azidobenzoyloxy-alkyl esters for use as a coating for printing plates, among other uses. In addition to these copolymers, radiation-sensitive reproduction layers can also contain organic binders which are developable in aqueous-alkaline solutions and customary additives. After irradiation and development, a relief image is produced on the support material.
The ink-repellent areas of virtually all of these prior are planographic printing plates either contain polysiloxanes or highly fluorinated organic compounds. Although the polysiloxanes show an excellent ink repellency, plates comprising substances of that kind have the disadvantage that the equipment and materials used for processing these plates are permanently soiled and thus have little utility for other purposes.
It is also a disadvantage of the hitherto available offset plates for waterless printing that, apart from a few exceptions, they operate with light-curable layers or compounds, i.e., they yield positive prints. Reversal is obtained by the fact that, as a rule, the exposed areas with the superposed ink-repellent layer remain on the support after development and printing is effected from the bared support or an ink-receptive sublayer.
One of the few negative-working plates for waterless offset printing known in the art is described in German Offenlegungsschrift No. 29 43 379. This plate comprises a support and a light-sensitive layer containing a 1,2-quinone diazide sulfonic acid ester of a phenol resin, with not more than 20% of the layer being soluble in ethanol. A silicone rubber layer is present on top of the light-sensitive layer. The plate must be developed with ethanol, since the ink-repellent cover layer is not wetted by aqueous developer solutions.